The present invention relates to accessing and controlling tape libraries for computer systems.
Tape libraries provide an effective and economical means for storing large amounts of information. Each tape library includes one or more tape drives performing access operations such as writing to tape and reading from tape. Information stored on magnetic tape is logically broken into tape volumes. The magnetic tape is typically packaged in tape cassettes or cartridges. There may be a one-to-one correspondence between tape volumes and cartridges, there may be multiple volumes on a single cartridge, or one volume may be split between several tape cartridges. In order to access information in a particular tape volume, the tape cartridge containing that volume must be loaded into a tape drive. In automated tape libraries, this is accomplished through a loading mechanism such as a robot. Larger information processing systems may contain more than one tape library. Cartridges may be passed between tape libraries manually or through the use of automated transport equipment. Tape volumes may be taken out of tape libraries manually through portals or may be copied onto a tape cartridge outside the tape library. Tape libraries are typically controlled by a tape library server which may perform functions such as tracking which cassettes hold each tape volume, tracking which library holds each cassette, controlling cassette loading and unloading mechanisms, controlling inter-library transport mechanisms, tracking cartridge use, managing data archiving, and the like.
Typically, tape libraries and the library server are directly connected to one or more host computers requiring access to tape volumes held within the tape libraries. Each host is connected to one or more tape drives through data links or tape channels. Each host is also connected to the library server. When a host computer wishes to access a particular tape volume, the host sends an access request for that volume to the library server. The library server determines if the requested volume is on a cassette within a tape library containing a tape drive connected to the requesting host. If not, the library server flags an operator or controls robots and transport mechanisms to move the tape cartridge to an appropriate tape library. The library server then commands a tape loading mechanism to mount the cartridge containing the requested volume into the host computer tape drive. The host computer can then write data to or read data from the mounted volume. When the host is through accessing the volume, the library server dismounts the cartridge.
There are many problems associated with the traditional connection of host computers to a tape library system. First, traditional systems lack flexibility. Adding additional storage resources, such as tape libraries and drives, requires running tape links between the new resources and host computers. The additional resources may further require software changes in the host computers to accommodate the increase in number and, possibly, differing types of storage. A second problem with traditional storage system configurations is the lack of complete connectivity between host computers and tape drives. If a particular volume requested by a host is located in a tape library to which the host does not have direct access, the host must wait for the relatively long period of time required to transfer the cassette containing the requested volume into a tape library to which the host has access. In addition to creating potentially long delays, the incomplete connectivity between hosts and libraries may result in underutilization of tape drives. A tape drive not being used by any host to which it is directly connected cannot be assigned to a different host. Another connectivity concern is library system equipment failure. If a tape drive or cassette loading mechanism fails, the tape system cannot be easily modified to offer uniform degraded performance to all host computers.
The present invention provides virtual tape libraries that may be accessed by computer elements such as host computers. Each computer element is provided access to at least one logical tape module. Each logical tape module appears to the computer element as a tape drive capable of accessing any volume on any cartridge in any tape library within the storage system.
A system implementing virtual tape libraries accessible by at least one host computer is provided. Each host computer has at least one computer link for writing data to and reading data from storage. The system includes at least one tape library for accessing tapes. Each tape library has at least one tape link carrying data written to or read from the tapes. A library server generates tape access commands for each tape library. A storage area network interfaces the host computers, tape libraries, and the library server. The storage area network maps logical tape access requests from each host computer into physical tape access requests for each tape library and the library server.
In an embodiment of the present invention, the storage area network includes at least one logical tape module for each host computer. Each logical tape module receives requests to access data on a tape volume. Each tape library is associated with at least one canonical tape module. Each canonical tape module responds to requests to access data on the tape volume. A management processor maps each logical tape module to a canonical tape module capable of responding to the tape volume access requests.
In another embodiment of the present invention, the management processor includes a proxy library having routines for servicing tape access requests. A client-side interface executes tape access request service routines based on tape access requests received from the host computers. A server-side interface generates library server commands based on the results of executed tape access request service routines. The client-side interface may exchange information with host computers through a first set of commands and the server-side interface may exchange information with the library server through a second set of commands.
A storage area network implementing virtual tape libraries is also provided. The storage area network includes logical tape modules. Each logical tape module presents a logical tape drive to a computer element communicating with the logical tape module. The storage area network also includes canonical tape modules. Each canonical tape module communicates with a physical tape drive. A data interconnect connects the logical tape modules with the canonical tape modules. A management processor maps each logical tape module requested by a computer element into at least one canonical tape module.
A method of accessing data stored on magnetic tape is also provided. A request to access a tape volume is received. A tape drive that may satisfy the tape access request is determined. The tape drive is reserved in a canonical tape module. Each request to access data on the tape volume is mapped to the canonical tape module in a logical tape module. Each mapped data access request is forwarded from the logical tape module to the canonical tape module.
In an embodiment of the present invention, a request to access the tape volume begins by receiving a request to mount the tape volume. A mount query is sent to a tape library server. The mount query response is received from the tape library server. A plurality of canonical tape module identifiers may be received in the mount query response, each canonical tape module identifier identifying a tape drive capable of satisfying the tape access request. One canonical tape module identifier is selected from the plurality of canonical tape module identifiers corresponding to the tape drive optimizing the tape access request.
In another embodiment of the present invention, reserving the tape drive includes receiving a request to reserve the tape drive in the canonical tape module. A request to reserve the tape drive is sent to a tape library containing the tape drive. A response indicating that the tape drive has been reserved is received and sent to a management processor.
A method of presenting virtual tape libraries to at least one host computer is also provided. Each host computer is connected to at least one logical tape module. Each tape library is connected to at least one canonical tape module. A request to access a tape volume is received from the host computer. The request specifies a logical tape module. The specified logical tape module is mapped to a canonical tape module which can access the requested tape volume.
The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.